Date of Award
Team nineteen was partnered with Hexagon Manufacturing Intelligence and tasked with the assignment of automating a ball bar fixture used in error mapping of coordinate measurement machines. This design report outlines the processes employed during the design by the team, with the long term goal of creating a functional prototype of the product. This semester work was done in conceptual design and analysis to meet the design specifications developed by Hexagon and Team 19. The culmination of this semesters work is presented in a Proof of concept, with the intent of fabrication and manufacture, along with redesign and optimization being completed in the coming semester.
Error mapping is a process employed in the calibration of CMMs. This process is done by placing a Bar Ball in 12 different positions within the measurable volume of the CMM and taking a measurements on the surface of each Ball. The center of each ball is calculated along with the length distance between centers. Analysis is done of the change in measured length of the Bar Ball in each position and an error map is created to offset the known errors. By utilizing this process CMMs can be accurate to less one micron.
The problem faced by Hexagon is that currently this error mapping process must be done by hand which leads to a very labor intensive process. The Bar Ball must be moved into placed, then measurements taken manually with the CMM. Hexagon has charged Team 19 with creating a solution to this problem by automating the process. The goal of this project is to create a machine that can placed within the CMM, and after initial set up, can carry out the entire error mapping process without any human interaction.
The design solution proposed by Team 19 is a four degree of freedom robotic manipulator. Three linkages with rotation at both the base of the machine and the center of the affixed Bar Ball provide access to all 12 of the required positions. The machine will utilize worm gear driven, DC motors in order to actuate each DOF of the manipulator, and will be controlled with an Arduino Mega AVR development microcontroller. The control software will be integrated into the system and work in tandem with the CMM control software PC-DMIS in order to completely automate the placement and measurement of the Bar Ball in the error mapping process.
Binek, Aaron; Costa, Jeffrey; Fields, Taylor; and Welsh, Jackson, "Hexagon Mechanized Ball Bar Fixture" (2017). Mechanical Engineering Capstone Design Projects. Paper 20.